Process control systems, like those used in chemical, petroleum or other processes, typically include one or more centralized process controllers communicatively coupled to at least one host or operator workstation and to one or more field devices via analog, digital or combined analog/digital buses. The field devices, which may be, for example, valves, valve positioners, switches and transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process such as opening or closing valves and measuring process parameters. The process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, uses this information to implement a control routine, and then generates control signals that are sent over the buses or other communication lines to the field devices to control the operation of the process. Information from the field devices and the controllers may be made available to one or more applications executed by the operator workstation to enable an operator to perform desired functions with respect to the process, such as viewing the current state of the process, modifying the operation of the process, etc.
Process control system applications typically include process control routines that can be configured to perform various functions or operations in a process control system. For example, process control routines may be used to control valves, motors, boilers, heaters, etc. Process control routines may also be used to monitor field devices, modules, plant areas, etc. and collect information associated with a process control system. Field devices used to implement the process control routines are typically coupled to one another and to a process controller via a data bus. Data buses have limited resources including limited bandwidth available for field devices and process controllers to communicate information to one another. To ensure that sufficient time is available on the data bus for all field devices and controllers to execute their respective functions and communicate information therebetween, schedules are generated to indicate when the controllers and the field devices should execute their respective functions.